Officials say dolphins are dying in record numbers off the eastern coast of the United States because of a viral infection.

Officials say 753 bottlenose dolphins have washed ashore along the U.S. Atlantic coast since July. They say in normal years only around 74 dolphins wash ashore in the same time period.

The deaths exceed a massive die-off that devastated the coastal dolphin population in the late 1980s. Scientists fear more deaths are likely in the coming months.

The deaths have been linked to an infection called morbillivirus, which suppresses immunity. The virus caused the previous Atlantic Coast die-off and is similar to a human virus that causes measles.

Officials say they are not sure how the virus was introduced into the dolphin population or why it is so lethal. They say washed up humpback whales and pygmy sperm whales have also tested positive for the virus this year.